BLEACHING AND DEINKING PROCESSES WITH REAGENT RECYCLE

A process for the alkaline hydrogen peroxide bleaching of radiata pine thermomechanical pulp has been investigated by recirculating residual peroxide and recovering a further quantity of peroxide by washing the pulp. The effects of recycling liquor on peroxide stability brightnes s development and strength properties were studied. These properties w ere not adversely affected by recycling the bleach liquor under typica l industrial conditions. The quantity of stabilizers used in the bleac hing stage may be reduced by over 50% by recycling bleach liquor: Fact ors minimizing the decomposition of hydrogen peroxide while providing adequate bleaching, were determined. A computer program was used to mo del recycling and recovery of residual hydrogen peroxide by washing to optimize chemical composition of the bleach liquor A dilute stream of hydrogen peroxide, similar to that recovered in a washing stage has b een used as a substitute for the fresh chemical in the deinking of old newsprint It appears that recovered hydrogen peroxide is as effective as fresh chemicals for deinking operations. A cost analysis of the pr ocess is presented, based on chemical consumption, which shows that th e new bleaching process is significantly more cost effective than eith er a two stage bleaching process or a conventional medium pulp concent ration process.